Out of curiosity, do anybody know why Plan9 designers chose lowercase variables over uppercase ones?

At first, given the different conventions between rc and sh (eg $path is an array, while $PATH is a string), I supposed Plan 9 designers wanted to prevent conflict with unix tools relying to the older conventions.

However, I'm not sure this was the main reason, as this also open to subtle issues: if a unix shell modifies $IFS and then invoke an rc script, such script will ignore the change and keep using the previous $ifs.

Do anyone know what considerations led to such design decision?

Giacomo